The present invention relates to a head-positioning system of a magnetic disk device, and particularly to that to be applied in a magnetic disk device provided with a fine-tracking actuator.
Conventionally, a combination of springs and carriages connected to a main actuator have been used for head-positioning of a magnetic disk device.
The controllable frequency band of head-positioning mechanism of this type is mainly defined by the oscillation frequency of a vibration mode of the head-positioning mechanism itself, and by suppressing the oscillation of the vibration mode making use of a notch filter, for example, a controllable frequency band of 600 to 700 Hz is attained.
Along with advancement of magnetic disks of high track density, however, further enlargement of the controllable frequency band is now earnestly required, and a two-stage actuator has been studied for replying to this requirement. In the two-stage actuator, a fine-tracking actuator is provided for each head besides the main actuator, which can move the head only a little but has a high-frequency vibration mode enabling to move the head in a wide frequency band.
However, the two-stage actuator has a problem that the fine-tracking actuator interferes with the main actuator and reaction of high-speed movement of the fine-tracking actuator may provoke the oscillation of the main actuator, and hence, the controllable frequency band of the fine-tracking actuator is also limited by the vibration mode of the main actuator.
For dealing with this problem, several proposals have been disclosed. In a Japanese patent application laid open as a Provisional Publication No. 11854/'93, a relative position of a tracking actuator to a linear motor of an optical head is detected, and the tracking actuator is feedback-controlled with a differential value of the relative position for suppressing auto-oscillation because of mutual interference.
In another Japanese patent application laid open as a Provisional Publication No. 174517/'93, a magnetic disk device having hybrid-servomechanism is disclosed, wherein tracking control is performed according to both a positional error signal detected by a reading head from a data recording surface and a positional error signal detected by a servo-head reading a servo-pattern recorded on a servo-pattern recording surface of the magnetic disk.
However, the first prior art of the Provisional Publication No. 11854/'93 needs a special detector for detecting relative position of the tracking actuator to the linear motor, which makes the mechanism complicated and a product cost thereof high because of increased numbers of parts, and the second prior art of the Provisional Publication No. 174517/'93 requires at least one servo-pattern recording surface, which degrades the data-formatting efficiency, especially of a slim-type magnetic disk device having but a few numbers of magnetic disks.